Under-fire Tory MP Geoffrey Cox is part of a scheme “designed specifically to avoid tax” – but has not declared it in his register of interests.

Millionaire Cox took advantage of lockdown rules to cast votes in Parliament remotely, while staying in the British Virgin Islands.

At the same time, he was earning hundreds of thousands of pounds from a second job helping the Caribbean tax haven with a corruption inquiry launched by the UK Foreign Office.

But openDemocracy can reveal that Cox, who is the former attorney general, also has an undeclared stake in a scheme called Phoenix Film Partners LLP, which was previously investigated by tax officials.

HMRC previously made some investors pay “accelerated payment notices” which are targeted at people “involved in avoidance schemes”.

The MP was questioned about his involvement in Phoenix Film Partners in 2014, but told the Mirror: “I am not going to comment on my private tax affairs.”

At the time, the Financial Times said HMRC had ruled that Phoenix had been designed specifically to avoid tax.

But now – amid fierce criticism of his financial activities – it has now emerged that the scheme is not listed on his register of interests.

Rules say that MPs must declare any interest of more than £70,000 in a limited liability partnership. Lower value interests also need to be declared if they “might reasonably be thought by others to influence his or her actions or words” as a parliamentarian.

Cox has never said how much his stake in Phoenix is worth, and there is no suggestion he has done anything illegal.

Yesterday, the Daily Mail revealed that Cox took advantage of lockdown rules to vote in Parliament remotely while 4,000 miles away.

The newspaper said he was in the Caribbean to work for Withers, an international law firm.

In total, Cox has earned more than £1m from outside legal work over the past year, on top of his £82,000 salary as a backbench MP.

This includes almost £900,000 from Withers and more than £130,000 for other legal work.

The Daily Mail reported that, as part of his role at Withers, Cox had been advising the government of the British Virgin Islands in an inquiry into whether there is government corruption in the tax haven.

The inquiry was launched by the UK to establish whether there is evidence of “corruption, abuse of office or other serious dishonesty that has taken place in public office in recent years”.

A senior Whitehall source told the newspaper that Cox was “pocketing hundreds of thousands of pounds to help stop the exposure of corruption in a Caribbean paradise”.

The MP joined Withers last year, where he works to “enhance its advice to both its private and overseas government clients”.

Announcing his appointment, the company’s CEO said: “His experience at the sharp end in government will be invaluable to us and to our clients”

Speaking to reporters yesterday, a Downing Street spokesman appeared to criticise the extent of Cox’s outside work, saying that MPs “should be visible in constituencies”.

“If they’re not doing that, they’re not doing their job and will rightly be judged on that by their constituents.”

The spokesman added: “It’s incumbent on MPs to be visible and to demonstrate to their constituents that they are acting on behalf of them. But it is up to our constituents to make that judgement.”

But the deputy prime minister, Dominic Raab, said Cox’s work in a tax haven was “a legitimate thing to do, as long as it’s properly declared”.

Geoffrey Cox did not respond to a request to comment.